1. Field of the Invention
The present invention relates generally to gas turbine engine fan assemblies and, more specifically, to a fan assembly having fan blades with circular arc dovetail roots that mate in circular arc dovetail slots in a disk of a fan rotor.
2. Discussion of the Background Art
A turbofan gas turbine engine used for powering an aircraft in flight includes a fan assembly having a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk. Ambient airflow is channeled between the blades and pressurized thereby for generating thrust for powering the aircraft in flight. The fan assembly typically includes a plurality of circumferentially spaced apart fan blades each having a dovetail root disposed in a complementary, axially extending dovetail groove or slot in a perimeter or rim of a rotor disk. The dovetail grooves are defined by dovetail posts and are complementary in configuration with the blade dovetail roots for radially retaining the blades to the rotor disk. The blades are also axially retained in the rotor disk to prevent axial movement of the blades in the upstream and downstream directions. A spinner is mounted to a front end of the fan assembly to provide smooth airflow into the fan.
A radially inner flowpath boundary for the airflow channeled between the blades is provided typically by integral platforms at the blade roots which circumferentially abut each other between adjacent fan blades. There are often reasons for increasing the airflow through the fan blades to increase the thrust without increasing or holding to a limit of a tip of the fan blade. An inner flowpath boundary, often referred to as the hub, is moved radially inwardly from an existing engine design or the engine is originally designed to have, what is referred to as, a low radius hub. Conventionally, a radial transition portion is a transition from a curved blade section at the flowpath to a straight shank at the top of the dovetail. Due to the low inner diameter of the flow path, the radial transition portion of the fan blade from the aerodynamic or curved portion of the blade to the dovetail root is significantly shortened. It is desirable to have a fan disk assembly for a low radius hub design which incorporates a circular arc dovetail root and slot to ensure an adequate footprint and load path into the disk.
The circular arc dovetail is arc shaped as disclosed in U.S. Pat. No. 5,123,813 which discloses circular arc dovetail slots and roots having centerlines in the form of arcs of a circle when viewing the disk radially.
A gas turbine engine rotor assembly includes a rotor disk with annular disk hubs circumscribed about a centerline wherein each of the hubs is connected to a disk rim by a web and substantially rounded web channels extend between the webs. The web channels have relatively wide channel maximum widths, extending axially between the webs, and relatively short channel lengths extending radially between the rim and the hubs. The channel maximum width is on the same order of magnitude as the channel length. A plurality of circumferentially spaced apart dovetail slots are disposed through the rim, extending circumferentially between disk posts, extending axially from a forward end to an aft end of the rim, and extending radially inwardly from a disk outer surface of the rim. Circumferentially extending annular burst slots extend radially through the rim into the dovetail slots between each adjacent pair of the webs. In the exemplary embodiment of the invention illustrated herein, the dovetail slots are circular arc dovetail slots.
Further embodiments include alone and in combination the following features or elements associated with the disk. An overhang extending axially forwardly from and located radially outwardly on each of the disk posts. A plurality of post holes extending axially aftwardly into the rim wherein each of the post holes extends axially aftwardly into a corresponding one of the disk posts. Forward and aft disk lugs extend radially outwardly from the posts along a disk outer surface of the rim. An annular forward extension having an annular forward flange and connected to an annular forward arm extending forwardly from a forward most one of the webs.
Other embodiments include the following. A one piece spinner attached to the forward flange of the forward extension at a location between a tip and an axially aft spinner end of the spinner. Non-integral platforms circumferentially disposed between the fan blades. A booster spool is connected to the rotor disk by a mounting plate therebetween and the platforms are radially retained to the disk and mounting plates by pins through holes in mounting lugs depending radially inwardly from the platforms.
Other embodiments include pairs of circumferentially oppositely facing retaining slots extend through the overhangs of circumferentially adjacent disk posts at an axial location where the overhangs begin extending axially forward from the rim. Retainers disposed in the pairs of the circumferentially oppositely facing retaining slots extend across the dovetail slot so as to axially retain the dovetail roots in the dovetail slots. Circular arc shaped spacers are disposed within corresponding ones the dovetail slots between dovetail slot bottom walls and axially extending root bottom surfaces of the fan blade dovetail roots. The spacers include features for exerting a radially outwardly directed force upon the blade dovetail root in order to limit relative motion between the fan blade and the disk. In one embodiment, these features include a backbone with dovetail lands wherein the backbone and the forward, mid, and aft dovetail lands, respectively, have bottom curved backbone surfaces continuous and co-extensive with the dovetail slot bottom wall.
Other embodiments include bladeout bumpers having circumferentially extending appendages on the forward disk lugs. The appendages extend circumferentially toward suction sides of airfoil sections of the fan blades. The fan blades include fan blade lightening holes extending radially outward through the fan blades and the appendages are axially located to ensure that the contact is made at an axial contact location between the fan blade lightening holes instead of at a fan blade lightening hole. Each of the bladeout bumpers axially spans at least between two hole centerlines of two adjacent fan blade lightening holes of a corresponding one of the fan blades.